Touch sensor devices (also commonly called touch pads or proximity sensors) are widely used in a variety of electronic systems. A touch sensor device is typically a sensitive surface that uses capacitive, resistive, inductive, optical, acoustic or other technology to determine the presence, location and or motion of one or more fingers, styli, and/or other objects. The touch sensor device, together with a finger or other object provides an input to the electronic system. For example, touch sensor devices are used as input devices for computers, such as notebook computers.
Touch sensor devices are also used in smaller devices, such as personal digital assistants (PDAs) and communication devices such as wireless telephones and text messaging devices. Increasingly, touch sensor devices are used in multimedia devices, such as CD, DVD, MP3, video or other media players. Many electronic devices include a user interface; or UI, and an input device for interacting with the UI. A typical UI includes a screen for displaying graphical and/or textual elements. The increasing use of this type of UI has led to a rising demand for touch sensor devices as pointing devices. In these applications the touch sensor device can function as a cursor control device, selection device, scrolling device, character/handwriting input device, menu navigation device, gaming input device, button input device, keyboard and/or other input device.
One issue in touch sensor device design is the efficient use of available space. In modern electronics, space is at a premium. This is particularly true for small devices, such as portable media players and wireless communication devices. In some previous touch sensor device designs the effective area on a touch sensor device, e.g., the area in which the position of an object can be accurately determined, was limited to a relatively small portion of the actual touch area. For example, in some designs the effective area was limited to approximately the region inside the center of the outermost electrodes. Outside of this area the position of objects cannot be accurately determined. The difference between the actual area of the touch sensor device and the effective area is thus wasted space. The wasted space increases the space required and the cost needed to provide a touch sensor device with a particular effective area. There remains a continuing need for improved touch sensor device designs that can provide improved space efficiency.